The Afghan immigrant accused of plotting a massive terror attack, involving bombs on New York City commuter trains -- possibly on the anniversary of 9/11 -- has arrived back in New York, thanks to the feds and the NYPD.

Accompanied by U.S. Marshals, Najibullah Zazi arrived at Teterboro Airport in a plane from Denver and was placed in an NYPD helicopter for further transport at about 5:40 pm. The chopper took him to the Brooklyn Army Terminal and he was put into a dark blue Chevy accompanied by heavily armed and armored agents.

Terror Suspect Najibullah Zazi Brought Back to NY

Najibullah Zazi was filmed shopping for chemicals that could be used to make a bomb, in a beauty supply store. (Published Friday, Sep 25, 2009)

Zazi was taken to Metropolitan Detention Center, a federal holding facility in Sunset Park, where he is expected to be held in solitary confinement and protective custody until his arraignment in federal court in Brooklyn on Tuesday.

Earlier today, U.S. prosecutor Tim Neff told a federal judge in Denver that Najibullah Zazi "was intent on being in New York on 9/11" for a possible terror attack.

Surveillance Camera Captures Zazi Shopping for Chemicals

Terror suspect Najibullah Zazi was seen shopping for elements to make a bomb -- in a beauty supply store. (Published Friday, Sep 25, 2009)

"The defendant was in the throes of making a bomb and attempting to perfect his formulation," Neff said. He called the evidence a "chilling, disturbing sequence of events."

U.S. Magistrate Judge Craig Shaffer ordered the 24-year-old Zazi held without bail pending his transfer to New York, where a federal grand jury indicted him on the terror charges, which carry a possible life sentence upon conviction.

The U.S. indictment says Zazi received explosives training from al-Qaida and bought large quantities of hydrogen peroxide and nail-polish remover at beauty supply stores to make bombs, possibly to detonate on New York City commuter trains.

Zazi has denied any involvement with terror.

Shaffer earlier dismissed a charge accusing Zazi of lying to federal authorities. Zazi was arrested Saturday on that charge — considered a holding charge until the federal indictment was handed down on Thursday.

Prosecutors told the judge Zazi posed a significant risk to the public and had few ties to the Colorado community, making him a flight risk.

Investigators have fanned out across the Denver area and New York City, going to beauty shops, home improvement stores and neighborhoods Zazi frequented looking for possible accomplices, while the government issued national terrorism warnings for sports complexes, hotels and transit systems.

A law enforcement official told The Associated Press on Thursday that Zazi had associates in New York who were in on the plot. Court papers say that during the summer, Zazi and three unidentified associates bought "unusually large quantities" of hydrogen peroxide and acetone — a flammable solvent found in nail-polish remover — from beauty supply stores in the Denver area, products with names like Ion Sensitive Scalp Developer and Clairoxide.

Zazi searched a Queens home improvement store's website for another ingredient needed to make a compound called TATP (Triacetone Triperoxide), the explosives used in the London bombings that killed over 50 people, prosecutors said.

Zazi has publicly denied being a terrorist since his arrest. He left a Denver court Thursday without commenting.

The government motion seeking to deny bail laid out a chronology of the alleged scheme, which prosecutors said had been in the works for over a year.

Zazi — a legal U.S. resident who immigrated in 1999 — began plotting as early as August 2008 to "use one or more weapons of mass destruction," when he "and others" traveled from Newark, N.J., to receive explosives training in Pakistan, prosecutors said.

Within days of returning from Pakistan in early 2009, he moved to the Denver suburb of Aurora, where he used a computer to research homemade bomb ingredients and to look up beauty supply stores where he could buy them, according to prosecutors.

A second law enforcement official who spoke on condition of anonymity because of the ongoing investigation said associates of Zazi visited Colorado from New York to help him buy the chemicals, using stolen credit cards to make the purchases before returning to New York.

Security video and receipts show that some of the purchases were made near a Colorado hotel, according to court papers. On Sept. 6 and 7, Zazi checked into a suite at the hotel with a kitchen and a stove, the papers say, and tried to contact an unidentified associate "seeking to correct mixtures of ingredients to make explosives."

"Zazi repeatedly emphasized in the communications that he needed the answers right away," the papers said. "Each communication" was "more urgent than the last."